1. Field of the Invention
The invention relates to the field of dry powder pharmaceuticals. The invention discloses methods of obtaining particles with improved aerodynamic performance or in which the active agent is more stable and efficiently delivered. More particularly, the present invention concerns methods for drying, particularly spray drying diketopiperazine-insulin (DKP-insulin) particles. The dry powders of the invention have utility as pharmaceutical formulations for pulmonary delivery.
2. Description of the Related Art
A number of different methodologies are employed in the art for preparing particles as a dry powder composition. These methodologies include, for example, lyophilization, evaporation, phase separation, and spray drying (see PCT Patent Application: WO 91/16038). In the manufacture of dry powder pharmaceuticals some methods start with the components in solution and form the particles of the powder by removing solvent. Other methods form particles in a separate, earlier step, such as by precipitation, and can result in a particle in suspension, which must then be dried. Methods such as lyophilization and evaporation are often used particularly for drying or removing a solvent from particles in suspension, whereas spray drying has more typically been used for particle formation from solution. For example, see U.S. Pat. Nos. 5,976,574; 5,985,248; 6,001,336; 6,051,256; 6,077,543; 6,365,190; 6,372,258; 6,423,344; 6,479,049; 6,509,006; 6,569,406; 6,572,893; 6,582,728; 6,838,076; and 6,896,906.
Lyophilization, or freeze drying, involves a process in which solvent, typically water, is removed from a product after it is frozen and placed under a vacuum, allowing the ice to change directly from solid to vapor without passing through a liquid phase. The process consists of three separate, unique, and interdependent processes; freezing, primary drying (sublimation), and secondary drying (desorption). During spray drying, a (generally aqueous) solution is introduced via a nozzle (e.g., a two fluid nozzle), spinning disc, or an equivalent device into a hot gas stream. Passage through the nozzle atomizes the solution into fine droplets. The heat energy supplied by the gas stream causes the evaporation of water or other solvents, thereby producing fine particles.
Drug delivery using substituted diketopiperazine microparticles has been described in U.S. Pat. Nos. 5,352,461; 5,503,852; 6,331,318; 6,395,774 and 6,663,898. Pulmonary delivery of diketopiperazine microparticles as dry powders is described in U.S. Pat. Nos. 5,503,852; 6,428,771; 6,444,226 and 6,652,885. Various methods for forming and loading diketopiperazine particles for drug delivery are disclosed in U.S. Pat. No. 6,444,226, U.S. patent application Ser. Nos. 11/532,063 and 11/532,065 both filed on Sep. 14, 2006, and U.S. Provisional Patent Application Ser. No. 60/717,524, filed on Sep. 14, 2005. Each of these documents is incorporated herein by reference for all they contain regarding diketopiperazines, diketopiperazine microparticles and their use in drug delivery. Dry powders made according to these teachings work well for pulmonary delivery; however there remains room for improvement of various pharmaceutic properties. The present invention serves to overcome the need in the art for obtaining improved particles having superior aerodynamics and providing more efficient delivery and greater stability of the active agent.